But it's not just the Iron Man vs. Thor dustup in the forest, or Captain America commanding the super-troops, or the most effective use yet of Hulk onscreen, or Black Widow ... 'nuf said ... that makes the movie an event. It's what happens when all these combustible elements come together, with the actors already associated with the roles and a bona fide comics nerd at the wheel. Or more than one.

“We have spectacle and special effects that are bigger than anything in some of our other movies combined,” says Marvel Studios president of production Kevin Feige, “but my favorite parts are those character interactions. The scene between (villain) Loki and Widow. The banter and arguments, the ideological conflict between Steve Rogers (Captain America) and Tony Stark (Iron Man).”

“Kevin is a geek,” says appreciative writer-director Joss Whedon, who would know. “He's a big old nerd who really understands comics, really understands movies, and knows the difference.”

Whedon is known for sharp dialogue and character development in the “Buffy the Vampire Slayer” TV series, “Firefly” and the hit Internet musical “Dr. Horrible.”

“He's got a pretty good life, that Joss Whedon,” Feige says. “He can do whatever he wants. (The effects are) not what people come out of the movie talking about; they come out talking about those character moments. That's what Joss' stories have; people always talk about the characters. They're hard-core sci-fi, hard-core fantasy. But it's always those moments that play out.”

“Only in the sense of, ‘Whoa, this is tiring,'” Whedon says. “Maybe there's something wrong with me, but it didn't flap me that I was doing this. I feel enormous pressure all the time as a storyteller. I don't feel pressure from budgets and stars. The problems are the exact same problems on any project: ‘We can't get this' or ‘That camera move wasn't as smooth as I hoped.' ... For the first three weeks I was literally saying, ‘This is more like directing an Internet musical than I'd imagined.' Everybody's schedules were a nightmare, and the paint was drying on the sets while we were shooting them. That was the only difference — this time we had paint for the sets.”

Evans describes Joss as “another comic-book geek.”

“Joss writes comic books. So any direction he wants to push the character, you never question — Joss knows.”

Evans had his own ice to break in donning the star-spangled uniform — and the six-movie deal that came with it.

“The way movies work is it's a one-at-a-time gig. If you do a movie and it explodes, and you're not coping with it terribly well, you have the opportunity to step back and regroup, get your head on straight,” says the buzz-cut, bearded Evans, looking more life-size than in his bulked-up Cap persona.

“The problem with these movies is, it's such a commitment, a contractual obligation, that if you're struggling with that new life, too bad. You've got to go and make another one. That just scared me. Six movies, they could spread that out over 10 years. I didn't know if I was ready to make a decision for a decade. So I was kind of scared, but I came around.”

Feige says of all the calls he has had to make from his celestial perch atop the Marvel Universe, casting has always been the scariest. He cites the nervous moments when they were “all in,” shooting “Avengers” with Evans and Hemsworth as cornerstone characters before their debut movies, “Captain America: The First Avenger” and “Thor,” had even came out. Luckily, those two films combined for more than $800 million in worldwide gross.

He marvels at how Evans, in particular, has embraced his character.

“His screen persona is so different from Steve Rogers, and so is his own life, frankly. He will talk about what a good man Steve Rogers is. Most actors want to talk about how flashy someone is, or ‘I've got the best one-liners' — Chris Evans, who has the one-liners in many movies, doesn't want that and wants to portray this good man.”

Evans says he was most surprised and excited by the Hulk scenes.

“All day, Ruffalo's in this ridiculous spandex suit looking absolutely obnoxious; you just don't know how it's going to turn out. ... So any time I saw (the finished) Hulk battles — the Hulk and Thor battle is just unbelievable.”

“That's why I actually did a little work on the first ‘Hulk.' I did just a couple days of tweaking stuff to help out, largely because it was Ang Lee,” he said. “I care deeply about the character, but I know he's also one of the most problematic in the Marvel Universe.

“I spent a lot of time thinking about ‘Hulk' movies and why I had problems with them. ... the idea he might really damage somebody we care about.”

Including Evans, who flashes that multimillion-dollar smile as he talks about playing superhero dress-up with a bunch of other folks.

“Certainly, to look around and you're not the only one in a silly outfit, it's fun,” he says. “I knew these characters. The first time I saw Hemsworth and Downey in the full thing, I was like, ‘Man, I love these characters, and I can't believe I'm working with them.' It's like a dream, it was like a summer camp or something.”